If you are performing DMA's *anywhere* in your code, while the sound
is playing, you risk pre-empting the CPU's interrupt handler from
being able to feed more sound when the existing sample completes.
That situation caused random, intermittant clicking in my code.
Basically, you really have to make sure that when the sound DMA
completes its' last transfer, and generates an interrupt so that it
can be given more sample-data, you really need to service it ASAP.
DMA's take higher precidence than CPU, and if active when the
interrupt is triggered, can cause a delay before the interrupt is
serviced, and thus, a click is heard once in a while. There may be
more reasons for these clicks, but that's the only problem I ran into
which caused them. I hope that helps lead to a solution...

Roger